Mixer performance is measured according to the bandwidth, noise characteristic, as well as dynamic range. The dynamic range is limited by noise and distortion products. An indicative measurement is the intermodulation intercept point or other similar criteria. Mixer and mixer designs have been based either on switching or small signal approximations to the modulating function. Due to the high harmonic content of switching and nonlinearities of the large signal functions, these mixers have been plagued by harmonic mixing, spurious responses, and intermodulation distortion. Furthermore, optimum mixer performance generally requires a constant 50 ohm nominal impedance across all ports. Commercially available high performance diode ring double-balanced mixers have a third order of input intermodulation intercept point of +35 dBm.
High frequency mixer and mixer applications which require doubly-balanced performance typically use the well-known diode ring type mixer or a variation thereof, which include active devices and transformers. The equipment, which includes mixers, is directly limited by the performance of the mixers. It is therefore desirable to improve equipment performance by improving the performance of double-balanced mixers while maintaining wide bandwidth characteristics and their simplicity and economy.